During the coagulation process, factor IXa (activated Christmas factor) and factor VIII (antihemophilic factor) interact in the presence of calcium ions and phospholipid to form a complex. This complex is then capable of converting factor X (Stuart factor) to factor Xa. The present investigations involve the isolation and characterization of factor X from human plasma and a study of its mechanism of activation by (1) factors VIII and IXa, (2) tissue factor and VII, (3) trypsin, and (4) the protease from Russell's viper venom. Another goal of this project will be to isolate and characterize factor VII from bovine sources and compare portions of its structure with prothrombin and factors IX and X. Another major goal of this research will be to carry out structural studies on factors IX and X isolated from cows treated with dicumarol in order to compare these proteins with normal factors IX and X.